package 二叉树;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Stack;

/**
 * 429. N-ary Tree Level Order Traversal
 * https://leetcode.com/problems/n-ary-tree-level-order-traversal/
 *
 * Given an n-ary tree, return the level order traversal of its nodes' values.
 *
 * Nary-Tree input serialization is represented in their level order traversal, each group of children is separated by the null value (See examples).
 *
 * Example 1:
 *           1
 *         / | \
 *        3  2  4
 *       / \
 *      5   6
 *
 * Input: root = [1,null,3,2,4,null,5,6]
 * Output: [[1],[3,2,4],[5,6]]
 *
 * Example 2:
 *
 *              1
 *        /  /  |   \
 *       2  3   4    5
 *         / \  |   / \
 *        6  7  8  9  10
 *           |  |  |
 *           11 12 13
 *           |
 *           14
 *
 * Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
 * Output: [[1],[2,3,4,5],[6,7,8,9,10],[11,12,13],[14]]
 *
 * Constraints:
 * The height of the n-ary tree is less than or equal to 1000
 * The total number of nodes is between [0, 10^4]
 *
 */
public class E_429_N叉树的层序遍历 {

    public List<List<Integer>> levelOrder(Node root) {
        List<List<Integer>> results = new ArrayList<>();
        if (root == null) return results;

        List<Node> previousLayer = Arrays.asList(root);
        while (!previousLayer.isEmpty()) {
            List<Node> currentLayer = new ArrayList<>();
            List<Integer> previousVals = new ArrayList<>();

            for (Node node : previousLayer) {
                previousVals.add(node.val);
                currentLayer.addAll(node.children);
            }

            results.add(previousVals);
            previousLayer = currentLayer;
        }
        return results;
    }

    /**
     * 使用递归
     */
    public List<List<Integer>> results = new ArrayList<>();
    public List<List<Integer>> levelOrder2(Node root) {
        if (root != null) traverseNode(root, 0);
        return results;
    }

    public void traverseNode(Node node, int level) {
        if (results.size() <= level) {
            results.add(new ArrayList<>());
        }
        results.get(level).add(node.val);
        for (Node children: node.children) {
            traverseNode(children, level+1);
        }
    }
}
